Pyrithiones (2-mercaptopyridine-N-oxide, salts thereof, and bis-2,2' derivatives) are known to be excellent biocides in paint formulations. Combinations of zinc pyrithione and cuprous oxide are known to be excellent antifouling agents when formulated into paints and paint bases (i.e., the paint before pigment addition) also containing resin, as disclosed, for example, in U.S. Pat. No. 5,057,153. Unfortunately, however, such paints may have a limited service life due to leaching of the biocide from the paint film during use.
Copper pyrithione is known to have lower solubility in water than zinc pyrithione. Such low solubility would provide an extended period of antimicrobial activity for copper pyrithione relative to zinc pyrithione during use. Unfortunately, copper pyrithione is not commercially available, possibly due to the fact that its manufacture is surprisingly more difficult than the readily available zinc pyrithione, sodium pyrithione and bis-2,2'-pyrithione and its adduct with magnesium sulfate. The present invention overcomes this problem of lack of commercial availability of copper pyrithione by providing for the generation of copper pyrithione in-situ in the paint formulation through the reaction of another pyrithione compound with cuprous oxide in the presence of a controlled amount of water. Such a solution would be highly desired by the paint manufacturing community.
Thus, the present invention provides a solution to the problem. Although individually cuprous oxide, copper pyrithione and other pyrithione compounds are all known biocides, the use of a combination of a pyrithione compound and cuprous oxide in the presence of a controlled amount of water in order to provide in situ generation of copper pyrithione biocide in a paint has not been known heretofore to the knowledge of the present inventors.